A number of memory devices, such as flash memory devices, use analog memory cells to store data. Each memory cell stores an analog value, also referred to as a storage value, such as an electrical charge or voltage. The storage value represents the information stored in the cell. In flash memory devices, for example, each analog memory cell typically stores a certain voltage. The range of possible analog values for each cell is typically divided into threshold regions, with each region corresponding to one or more data bit values. Data is written to an analog memory cell by writing a nominal analog value that corresponds to the desired one or more bits.
The analog values stored in memory cells are often distorted. The distortions are typically due to, for example, back pattern dependency (BPD), noise and inter-cell interference (ICI). A number of techniques have been proposed or suggested for mitigating the effect of ICI by reducing the capacitive coupling between cells. Flash memory devices typically employ only hard-decision read operation. The analog threshold voltage (Vt) signal that represents the stored data typically cannot be sensed accurately without performing many read operations. In a flash storage system comprised of a flash controller and flash memory devices, if normal decoding fails, a soft read retry procedure can be employed with a number of hard-decision read operations.
A need remains for improved ICI mitigation techniques that reduce ICI using soft information obtained during the soft read retry procedure. A further need exists for ICI mitigation techniques for a given target cell that re-uses the soft information obtained during the soft read retry procedure for the target cell and only performs additional reads for aggressor cells.